Process for producing electrical insulating objects



process for producing electrical insulating Patented Sept fi, 12922.

UNHTED STATES intense PATENT @FFHQE.

AUGUS'I SIDLER, 0F ZURICH, SWITZERLAND.

3T0 Drawing.

trical Insulating Objects; and I do hereby declare the following to be a clear, full, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to improvements in a process for producing electrical insulating objects.

The object of. the present invention is a objects of slate. Slate has already been used for manufacturing electrical insulators in its natural state in the shape of slabs or by forming objects of a material composed of ground slate and an admixture of a binding material and treating them bya pressing operation. Such insulators are only suited for low tension. An addition of asbestos increases the insulating power only sli htly.

ccording to the present invention electrical insulating objects are produced by melting natural slate, casting it into moulds and cooling it slowly.

The objects produced in this manner are of-a jet black colour and of a very compact vitreous structure. -They show the surprising feature that they are able to resist very high tensions like the best insulators made of porcelain.

Refractory slates may be treated advantageously by adding fluxes such as soda, potash and the like in order to improve the economy of the'process.

Such a process may be carried out for ex- Application filed march 23, 1921. Serial No. 454,930.

ample by grinding the slate finely, melting it in'furnaces similar to those .used in manufacturing glass, casting it into moulds and cooling it very carefully and slowly in order to revent the formation of cracks. This coo ingprocessis best carried out in similar furnaces (annealing furnaces) as those used in the glass industry. If the slate contains a large percentage of quartz, lime may be added to prevent too strong a vitrifying ac tion. A strong vitrification enhances the formation of cracks which are, as is well known, inadmissible with electric insulators.

Experiments have shown that insulating slabs of 3 m/m thickness and produced in the manner described above will stand a tension of 25000 volts.

I claim:

1. A process for producing electrical in-. sulating objects, consisting of melting natural slate, casting said slate into moulds and cooling the molten mass slowly.

2. A process for producing electrical insulating objects, consistin of grinding finely natural slate, melting sai slate, casting the molten mass into moulds and cooling it slowly.

3. A process for producing electrical insulating objects, consisting of meltin natural slate to ether with additions o fluxes, casting said slate into moulds and 

